dmsetup: fix stats report command output

dmsetup: fix stats report command output

Since the stats handle is neither bound nor listed before the
attempt to call dm_stats_get_nr_regions(), it will always return
zero: this prevents reporting of any dmstats regions on any
device.

Remove the dm_stats_get_nr_regions() check and instead rely on
the correct return status from dm_stats_populate() which only
returns 0 in the case that there are regions to inspect (and
which logs a specific error for all other cases).

Reported-by: Bryan Gurney <bgurney@redhat.com>